Shop Windows to the Universe

This is a cutaway drawing of the proposed structure of Ganymede's interior.
Click on image for full sizeNASA

Differentiation

Differentiation is a scientific term which really means "to separate". In their earliest history, elements which made the planets would part into separate regions, if the planet were warm enough. This is the akin to the process whereby an oil & vinegar salad dressing will part into regions made only of oil and only of vinegar.

Planetary elements which separate include iron, which is heavy and silicate rock, which is lighter. Iron falls to the center of a planet and forms a core, silicate material stays in the middle, ice stays near the top, as shown in this drawing of the moon Ganymede.

Earth/Mars are examples of contiguous planets which did/did not differentiate early in their histories. Ganymede/Callisto are examples of contiguous moons which did/did not differentiate early in their histories. The lack of differentiation may say something about how warm these planets were upon formation.

You might also be interested in:

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more

Minerals are the building blocks of rocks. They are non-living, solid, and, like all matter, are made of atoms of elements. There are many different types of minerals and each type is made of particular...more

Also, prior to the official "beginning" of the Earth or start of the Archean age, the Earth turned inside out! That's right. Iron is heavy. As soon as the Earth became warm enough, the heavy iron which...more

The Archean is the name of the age which began with the forming Earth. This period of Earth's history lasted a long time, 2.8 billion years! That is more than half the expected age of the Earth! And no...more

The insides of most of the moons and planets separated while they were forming out of the primitive solar nebula. Measurements by the Galileo spacecraft have been shown that Callisto is the same inside...more

An important new result from the Mars Global Surveyor (MGS) mission is the definite confirmation of the presence of a magnetosphere around Mars. Previous missions did not make really good measurements...more

AU stands for Astronomical Units. It is a useful way to measure the distances in interplanetary space. It is the distance between the Earth and the Sun, which is about 93 million miles. For reference,...more